The present invention relates a method for forming a dielectric film in general. More particularly, it relates to a method for forming a high density dielectric film by chemical vapor deposition.
Conventional semiconductor devices comprise a semiconductor substrate, a plurality of inter-metal dielectric (IMD) layers and conductive patterns. The conductive patterns comprise conductive lines separated by the inter-metal dielectric layers, and a plurality of interconnect lines, such as bus lines, bit lines, word lines and logic interconnect lines. Furthermore, the conductive patterns on different layers are electrically connected by a conductive plug filling a via hole.
Aluminum and aluminum alloys have been the most widely used interconnection metallurgies for integrated circuits. It has become increasingly important, however, that metal conductors forming interconnections between devices as well as between circuits in a semiconductor have low resistivity for faster signal propagation. Copper is preferred for its low resistivity as well as for resistance to electromigration (EM) and stress voiding properties for very and ultra large scale integrated (VLSI and ULSI) circuits.
In conventional metal interconnect methodology, inter-metal dielectric layers must be subsequently formed on the conductive patterns serving as capping layer on the exposed surface of the conductive patterns (such Cu, Al, or alloy thereof). The inter-metal dielectric layers, such as silicon nitride, however, deposited by conventional plasma enhanced chemical vapor deposition (PECVD), exhibit poor adhesion to the conductive patterns surface. Consequently, the inter-metal dielectric layer is vulnerable to removal, as by peeling due to scratching or stresses resulting from subsequent deposition of layers. As a result, the conductive pattern, for example a Cu interconnect member, is not entirely encapsulated resulting in diffusion adversely affecting device performance and decreasing the electromigration resistance of the Cu interconnect member. Moreover, conventional PECVD dielectric layers have a density of about 2.62 g/cm3 and, hence, are not particularly effective as an etch stop layer during formation of interconnects for subsequent metallization levels.
As design rules extend deeper into the submicron range, e.g., to about 0.18 micron and under, the reliability of interconnect pattern becomes particularly critical. The adhesion of IMD layers to metal interconnects and the accuracy of interconnects for vertical metallization levels require even greater reliability. Thus, a method for forming a high density dielectric film with improved adhesion is desirable.